Determine whether to rebuild track metadata to determine whether a track format table has a track format code for the track format metadata

ABSTRACT

Provided are a computer program product, system, and method for managing read and write requests from a host to tracks in storage cached in a cache. A determination is made whether track format table support information for a track indicates that a track format table was previously determined to have or not have the track format code for track format metadata. Track format metadata for the track is rebuilt to determine whether the track format table includes a track format code for the rebuilt track format metadata when the track format table support information indicates that the track format table was previously determined to have a track format code for the track. The track format metadata is not rebuilt when the track format table support information indicates that the track format table was previously determined to not have a track format code for the track.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a computer program product, system, andmethod to determine whether to rebuild track metadata to determinewhether a track format table has a track format code for the trackformat metadata.

2. Description of the Related Art

In a storage environment, a host system may communicate a read/writerequest to a connected storage system over network channel through anetwork adaptor. If the data is in a cache of the storage system, i.e.,a read hit, then the data may be returned quickly to the host system.This reduces the delay in returning requested data to a host I/Orequest. However, if the requested data is not in the cache of thestorage system, then there may be significant latency realized while thestorage system needs to retrieve the requested data from storage toreturn. Further, the thread or task executing the host read request mayhave to be context switched and deactivated in order to allow the hostsystem to process further I/O requests. When the data is returned to theread request, then the task must be reactivated and data for the taskmust be returned to registers and processor cache to allow processing ofthe returned data for the read request.

There is a need in the art for improved techniques for processing hostread/write requests to the cache.

SUMMARY

Provided are a computer program product, system, and method for managingread and write requests from a host to tracks in storage cached in acache. A determination is made whether track format table supportinformation for a track indicates that a track format table waspreviously determined to have a track format code for track formatmetadata for the track or was determined to not have the track formatcode for the track format metadata. Track format metadata for the trackis rebuilt to determine whether the track format table includes a trackformat code for the rebuilt track format metadata in response todetermining that the track format table support information indicatesthat the track format table was previously determined to have a trackformat code for the track. The track format metadata is not rebuilt todetermine whether the track format table has a track format code for thetrack format metadata in response to determining that the track formattable support information indicates that the track format table waspreviously determined to not have a track format code for the track.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a storage environment.

FIG. 2 illustrates an embodiment of a track format table entry.

FIG. 3 illustrates an embodiment of a cache control block.

FIG. 4 illustrates an embodiment of a Least Recently Used (LRU) list oftracks in the cache.

FIG. 5 illustrates an embodiment of operations to process a read/writerequest received on a first channel, such as a bus interface.

FIG. 6 illustrates receive an embodiment of operations to process aread/write request received on a second channel, such as a network.

FIG. 7 illustrates an embodiment of operations to close track metadataand determine a track format code for the track in cache of the closedtrack metadata.

FIG. 8 illustrates an embodiment of operations to invalidate a metadatatrack.

FIG. 9 illustrates an embodiment of a storage environment havingmultiple processing nodes.

FIG. 10 illustrates an embodiment of operations to failover from oneprocessing node in the storage system to another processing node.

FIG. 11 illustrates an embodiment of operations to determine whether torebuild track format metadata and determine a track format code for thetrack format metadata.

FIG. 12 illustrates an embodiment of a computer architecture used withdescribed embodiments.

DETAILED DESCRIPTION

In a storage environment, a host system may first communicate aread/write request to a connected storage system over a fast channel,such as a bus interface, such as the Peripheral Component InterconnectExpress (PCIe) interface. For a read/write request over the fast channelwhich is supposed to complete within a threshold time, the host systemholds the application thread for the read/write request in a spin loopwaiting for the request to complete. This saves processor timeassociated with a context swap, which deactivates the thread andreactivates the thread in response to an interrupt when a response tothe read/write request is received. If the data for the read/writerequest sent on the fast channel is not in cache, then the storagesystem may fail the read/write request and the host system maycommunicate the same read/write request over a storage area network viaa host adaptor, which is slower than processing the I/O request over thebus, e.g., PCIe interface. Communicating the read/write request over thesecond channel requires the host system to perform a context switch fromthe task handling the read/write request to another task while waitingfor the read/write request to complete. Context switching is costlybecause it requires the processor running the task to clear allregisters and L1 and L2 caches for the new task, and then whencompleting the new task, reactivate the context switched task and returnthe state data to the registers and L1 and L2 caches for the task thatwas context switched while waiting for the read/write request tocomplete.

Certain read/write operations need to be completed within a thresholdtime, else they are failed. The storage system will have to access trackmetadata to process a request to a track. The track metadata providesinformation on the format of data and layout of records in the trackthat are needed in order to perform reads and writes to the track.However, the reading of the track metadata from the storage comprises asubstantial portion of the latency in processing read/write request.Described embodiments provide improvements to cache technology thatreduce cache operation latency by including a track format code in thecache control block for a track in the cache. This track format code maybe used for fast access to the track format from a track format tablewithout having to read the track metadata from storage. By eliminatingthe need to read the track metadata from a metadata track in storage todetermine the track layout, described embodiments increase thelikelihood that read/write requests on the first channel that need to becompleted within a threshold time are completed by accessing the tracklayout information for a track from the track format table, associatingtrack format codes with track format information for common trackformats.

With described embodiments, a read/write request to a target track on achannel requiring that the request be completed within a threshold timeis processed if the track format code for the target track is within thecache control block for the target track. Using the track format code toaccess the track format metadata from the track format table reduces thelatency of access to the track format metadata to allow the read/writerequest to complete within the time threshold. This keeps the time thehost thread is spinning on the read/write request task for theread/write request sent on the bus interface within an acceptable timethreshold. However, if the cache control block for the target track doesnot have a valid track format code, then the read/write request on thefirst channel is failed because it is unlikely the read/write requestcan complete within the threshold time given that the track formatmetadata will have to be retrieved from the storage. Failing theread/write request on the first channel, causes the host to redrive theread/write request on the second channel. The processing of theread/write request on the second channel reads in the track metadatafrom the storage to allow for processing the read/write request andadding the track format code to the cache control block for the targettrack.

Further, described embodiments provide track format table supportinformation on the results of a prior determination of whether the trackformat table provided a track format code for the track format metadata,such as indication that there was or was not a track format code in thetrack format table for the track format metadata, or that the trackformat code was invalidated without making a determination whether thetrack format table included a code for the track format metadata. Thissupport information may then later be used to determine whether toexpend processing resources to rebuild track metadata to determinewhether the track format table provides a track format code when thetrack format code is currently invalid. This support informationoptimizes the process by only rebuilding the track metadata to make thisdetermination if there is a likelihood the track format table doesprovide a track format code for the track format metadata, such as if atrack format code was previously determined for the track formatmetadata or the track format metadata was invalidated withoutdetermining whether the track format table provided a track format codefor the track format metadata. However, if the support informationindicates that the track format table is unlikely to provide a trackformat code for the track format metadata, such as if the supportinformation indicates that in a previous determination the track formattable did not provide a track format code for the track format metadata,then the track metadata will not be rebuilt because it is unlikely,given the previous determination, that a track format code will be foundin the track format table. In this way, processor resources areoptimized by using the track format table support information todetermine when the track format metadata will be rebuilt to determine ifthere is a track format code in the track format table.

FIG. 1 illustrates an embodiment of a storage environment in which ahost 100 directs read and write requests to a storage system 102 toaccess tracks in volumes configured in storage devices 104 in a diskenclosure 106. The host 100 includes a processor complex 108 of one ormore processor devices and a memory 110 including an operating system111 executed by the processor complex 108. The host operating system 111generates read and write requests to tracks configured in the storagedevices 104. The host 100 includes hardware to communicate read andwrite requests on two different channels. A first channel is a businterface, such as a Peripheral Component Interconnect Express (PCIe),including a bus 112, a bus switch 114 to connect one or more devices onthe bus 112, including the processor complex 108, a memory system 110,and a bus host adaptor 116 to extend the bus interface over an externalbus interface cable 118 to the storage system 102. Additional businterface technology to extend the bus interface may be utilized,including PCIe extender cables or components, such as a distributed PCIeswitch, to allow PCIe over Ethernet, such as with the ExpEthertechnology. A second channel to connect the host 100 and storage system102 uses a network host adaptor 120, connected to the bus 112, thatconnects to a separate network 122 over which the host 100 and storagesystem 102 additionally communicate. The first channel through the businterface may comprise a faster access channel than the network 122interface through the network host adaptor 120.

The storage system 102 includes a bus interface comprising a bus 124 a,124 b, a bus switch 126 to connect to endpoint devices on the bus 124 a,124 b, and a bus host adaptor 128 to connect to the external businterface cable 118 to allow communication over the bus interface to thehost 100 over the first channel. The storage system 102 includes anInput/Output bay 130 having the bus host adaptor 128, one or more deviceadaptors 132 to connect to the storage devices 104, and one or morenetwork host adaptors 134 to connect to the network 122 and hostsystems.

The storage system 102 includes a processor complex 136 of one or moreprocessor devices and a memory 138 having a cache 140 to cache tracksaccessed by the connected hosts 100. The memory 138 includes a cachemanager 142 and a storage manager 144. The storage manager 144 managesaccess requests from processes in the hosts 100 and storage system 102for tracks in the storage 104. The devices 136, 138, 128, 132, and 134connect over the bus interface implemented in the bus lanes 124 a, 124 band bus switch 126.

The cache manager 142 maintains accessed tracks in the cache 140 forfuture read access to the tracks to allow the accessed tracks to bereturned from the faster access cache 140 instead of having to retrievefrom the storage 104. Further, tracks in the cache 140 may be updated bywrites. A track may comprise any unit of data configured in the storage104, such as a track, Logical Block Address (LBA), etc., which is partof a larger grouping of tracks, such as a volume, logical device, etc.

The cache manager 142 maintains cache management information 146 in thememory 138 to manage read (unmodified) and write (modified) tracks inthe cache 140. The cache management information 146 may include a trackformat table 200 having track format codes for common track formatdescriptors providing details of a layout and format of data in a track;track index 148 providing an index of tracks in the cache 140 to cachecontrol blocks in a control block directory 300; and a Least RecentlyUsed (LRU) list 400 for tracks in the cache 140. The control blockdirectory 300 includes the cache control blocks, where there is onecache control block for each track in the cache 140 providing metadataon the track in the cache 140. The track index 148 associates trackswith the cache control blocks providing information on the tracks in thecache 140. Upon determining that the cache LRU list 400 is full or hasreached a threshold level, tracks are demoted from the LRU list 400 tomake room for more tracks to stage into the cache 140 from the storage104.

In certain embodiments, there may be multiple hosts 100 that connect tothe storage system 102 over the first and second channels to accesstracks in the storage devices 104. In such case, the storage system 102would have at least one bus host adaptor 128 to connect to the businterface 118 of each connected host 100 and one or more network hostadaptors 134 to connect to the network host adaptors 120 on the hosts100.

In one embodiment, the bus interfaces 112, 114, 116, 118, 124 a, 124 b,126, and 128 may comprise a Peripheral Component Interconnect Express(PCIe) bus interface technology. In alternative embodiments, the businterfaces 112, 114, 116, 118, 124 a, 124 b, 126, and 128 may utilizesuitable bus interface technology other than PCIe. The bus host adaptors116 and 128 may comprise PCIe host adaptors that provide the interfaceto connect to the PCIe cable 118. The network 122 may comprise a StorageArea Network (SAN), a Local Area Network (LAN), a Wide Area Network(WAN), the Internet, an Intranet, etc., and the network host adaptors120, 134 provide the network 122 connections between the hosts 100 andstorage system 102.

The storage system 102 may comprise a storage system, such as theInternational Business Machines Corporation (IBM®) DS8000® and DS8880storage systems, or storage controllers and storage systems from othervendors. (IBM and DS8000 are trademarks of International BusinessMachines Corporation throughout the world). The host operating system111 may comprise an operating system such as Z Systems Operating System(Z/OS®) from International Business Machines Corporation (“IBM”) orother operating systems known in the art. (Z/OS is a registeredtrademark of IBM throughout the world).

The storage devices 104 in the disk enclosure 106 may comprise differenttypes or classes of storage devices, such as magnetic hard disk drives,solid state storage device (SSD) comprised of solid state electronics,EEPROM (Electrically Erasable Programmable Read-Only Memory), flashmemory, flash disk, Random Access Memory (RAM) drive, storage-classmemory (SCM), etc., Phase Change Memory (PCM), resistive random accessmemory (RRAM), spin transfer torque memory (STT-RAM), conductivebridging RAM (CBRAM), magnetic hard disk drive, optical disk, tape, etc.Volumes in a storage space may further be configured from an array ofdevices, such as Just a Bunch of Disks (JBOD), Direct Access StorageDevice (DASD), Redundant Array of Independent Disks (RAID) array,virtualization device, etc. Further, the storage devices 104 in the diskenclosure 106 may comprise heterogeneous storage devices from differentvendors and different types of storage devices, such as a first type ofstorage devices, e.g., hard disk drives, that have a slower datatransfer rate than a second type of storage devices, e.g., SSDs.

FIG. 2 illustrates an embodiment of a track format table entry 200 _(i)in the track format table 200, which includes a track format code 202and the track format metadata 204. In certain embodiments Count Key Data(CKD) track embodiments, the track format metadata 204 may comprise atrack format descriptor (TFD) indicating a number of records in thetrack, a block size, a number of blocks in the track, a data length ofeach of the records, and a control interval size indicating an amount ofdata that is read or written atomically as a unit, number of blocks in acontrol interval, and whether a control interval spans two tracks, andother information. The track format code 202 may comprise an index valueof the index entry 200 _(i) in the track format table 200. For instance,if there are 32 track format table entries 200 _(i), then the trackformat code 202 may comprise 5 bits to reference the different possiblenumber of 32 entries 200 _(i).

FIG. 3 illustrates an embodiment of a cache control block 300 _(i) forone of the tracks in the cache 140, including, but not limited to, acache control block identifier 302, such as an index value of the cachecontrol block 300 _(i); a track ID 304 of the track in the storage 104;the cache LRU list 306 in which the cache control block 300 _(i) isindicated; an LRU list entry 308 at which the track is indicated; acache timestamp 310 indicating a time the track was added to the cache140 and indicated on the LRU list 306; additional track metadata 312typically maintained for tracks stored in the cache 140, such as a dirtyflag indicting whether the track was modified; a track format code 314comprising one of the track format codes 202 of the track formatmetadata 204 describing the layout of data in the track 304 representedby the cache control block 300 _(i); a track format code valid flag 316indicating whether the track format code 314 is valid or invalid; andtrack format table support information 318 indicating whether the trackformat table 200 previously provided a track format code for the trackor a reason why the track format code was invalidated, such as due to adetermination the track format table 200 did not provide a track formatcode 202 for the track format metadata, or that the track format codewas invalidated without determining whether the track format table 200provided a track format code 202 for the track format metadata.

FIG. 4 illustrates an embodiment of an LRU list 400 _(i), such as havinga most recently used (MRU) end 402 identifying a track most recentlyadded to the cache 140 or most recently accessed in the cache 140 and aleast recently used (LRU) end 404 from which the track identified at theLRU end 404 is selected to demote from the cache 140. The MRU end 402and LRU end 404 point to track identifiers, such as a track identifieraddress or a cache control block index for the track, of the tracks thathave been most recently added and in the cache 140 the longest,respectively, for tracks indicated in that list 400.

FIG. 5 illustrates an embodiment of operations performed by the cachemanager 142 and storage manager 144 to process a read/write request to atarget track received on a first fast channel, such as the PCIe businterface via bus host adaptor 128. Upon receiving (at block 500) theread/write request at the bus host adaptor 128, if (at block 502) thetarget track is not in the cache 140, then the storage manager 144returns (at block 504) fail to the read/write request on the firstchannel or bus host adaptor 128 to the host 100, which causes the host100 to retry the read/write request on the second channel or networkhost adaptor 120, 134. Failure is returned because if the target trackis not in the cache 140, then the target track and track metadata needsto be staged into cache 140, which would likely exceed the timethreshold for read/writes on the first channel, where the host processoris spinning on the thread of the read/write request. If (at block 502)the target track is in the cache 140 is a write and if (at block 508)the write modifies the track format, then the cache manager 142 sets (atblock 510) the track format code valid flag 316 to invalid. The cachemanager 142 indicates (at block 512) in the track format table supportinformation 318 that no determination was made whether the track formattable 200 supports the new track format metadata resulting from thewrite to the track modifying the track format. The storage manager 144then returns (at block 504) fail to the host 100 because the trackmetadata needs to be read from the storage 104 to update with themodified track format.

If (at block 506) the read/write request is a read or if (at block 508)the request is a write that does not modify the track format, then thecache manager 142 determines (at block 514) if the track format codevalid flag 316 is set to valid. If so, then the cache manager 142determines (at block 516) the track format metadata 204 in the trackformat table 200 corresponding to the track format code 314 in the cachecontrol block 300 _(i). The cache manager 142 uses (at block 518) thetrack format layout indicated in the determined track format metadata204 to process the read or write request to the target track in thecache 140. If the request is a write, a dirty flag 312 in the cachecontrol block 300 _(i) may be set to indicate the track is modified. If(at block 514) the track format code valid flag 316 is invalid, meaningthere is no fast access to track format information available throughthe track format code 314, then the storage manager 144 returns (atblock 504) fail on the bus interface to the bus host adaptor 128 becausethe track format table 200 cannot be used, and the track metadata needsto be read from the storage 104, which would introduce too much latencyfor the fast read/write on the first channel.

With the embodiment of operations of FIG. 5, during a fast write overthe bus interface or first channel, if the track format metadata may beaccessed without latency through the track format table 200, then theread/write request is allowed to proceed when the transaction can beprocessed very quickly because the track metadata can be obtaineddirectly from the track format table 200 through the track format code314, without having to read the track metadata from storage 104.However, if the cache control block 300 _(i) does not have a valid trackformat code 314 to allow low latency access of track format metadata,then the read/write request is failed because the transaction will notlikely complete within a fast time threshold. This determination isimportant to avoid host delays in processing other tasks while the hostprocessor is spinning on the thread handling the read/write requestwhile waiting for the read/write request to complete. If the trackmetadata can be accessed from the track format table 200 than there is ahigh likelihood the read/write can complete on the bus interface channelwithin the time required to avoid the host processor holding the threadfor too long, which causes other I/O requests to be queued and delayed.If the track metadata cannot be accessed from the track format table 200and needs to be read from the storage 104, then it is unlikely theread/write request will complete within the time threshold for the hostprocessor to spin on the thread for the read/write request, and failureis returned. Returning failure when the track metadata cannot beobtained from the track format table 200 causes the host thread waitingon the read/write request task to be deactivated and the host processormay context switch to processing other tasks, and then the read/writerequest is retried on the second network channel during the contextswitch.

Further, indication is made at block 512 that no determination was madeas to whether the track format table 200 supports the new modified trackformat metadata, so that this determination of the track format code forthe track format metadata may be made later, because supportability isunknown at this point.

FIG. 6 illustrates an embodiment of operations performed by the cachemanager 142 and storage manager 144 to process a read/write request to atarget track received on a second channel, such as the network 122 onnetwork host adaptor 134. Upon receiving (at block 600) the read/writerequest, if (at block 602) the target track is not in the cache 140,then the cache manager 142 stages (at block 604) the track from thestorage 104 to the cache 140 and reads (at block 606) the track metadatafor the target track from the storage 104 to determine the track format,e.g., size of blocks, control interval, layout of records on the track,etc. If (at block 608) the read/write request is a write and if (atblock 610) the write modifies the track format, then the cache manager142 updates (at block 612) the track metadata to indicate the modifiedtrack format and sets (at block 614) the track format code valid flag316 to invalid. The cache manager 142 indicates (at block 615) in thetrack format table support information 318 that no determination wasmade whether the track format table 200 supports the new track formatmetadata resulting from the write to the track modifying the trackformat. This indication is made to later provide information that thereis still a likelihood that a track format code 202 may be supported inthe track format table 200 for the new modified track format, because nosuch determination has been made at this point. The track metadata 312is further updated (at block 616) to indicate the track is modified ordirty. If (at block 608) the request is a read or from block 616, thecache manager 142 uses (at block 618) the track format layout indicatedin the track format metadata to process the read or write request to thetarget track in the cache 140.

If (at block 602) the target track is in the cache 140 and if (at block630) the track format code valid flag 316 is set to valid, then thecache manager 142 determines (at block 632) the track format metadata204 in the track format table 200 corresponding to the track format code314 in the cache control block 300 _(i) for the target track. From block632, control proceeds to block 608 to process the read/write request. If(at block 630) the track format code valid flag 316 is set to invalid,then control proceeds to block 606 to read the metadata for the trackform the storage 104 to determine the track format layout.

With the embodiment of FIG. 6, when the read/write request is receivedon the second slower channel, such as over the network 122, where thehost operating system 111 would have performed a context switch for thethread handling the read/write request, the cache manager 142 may readthe track metadata from the storage 104 to determine the track layout toprocess the request. During this time, the host processing of furtherhost requests is not delayed because the host thread handling theread/write request is context switched and not active, until theread/write request returns complete.

FIG. 7 illustrates an embodiment of operations performed by the cachemanager 142 when closing the track metadata for a track in the cache140, which involves destaging the track metadata to the storage 104 ifchanged. Upon closing (at block 700) the track metadata for a track inthe cache 140, the cache manager 142 processes (at block 702) the trackmetadata to determine a track format or a layout of data in the track.If (at block 704) the track format table 200 does not have a trackformat metadata 204 matching the determined track format from the trackmetadata, which may happen if the determined track format is irregular,then the track format code valid flag 316 is set (at block 706) toinvalid and the track format table support information 318 is set (atblock 708) to indicate the track format table 200 does not include atrack format code 202 for the track format metadata of the track. Insuch situation, read./write requests to the track having an irregularformat are only processed when received through the second channel vianetwork host adaptor 134.

If (at block 704) the track format table has a track format metadata 204matching the determined track format from the track metadata, then thecache manager 142 determines the track format code 202 for thedetermined track format metadata 204 in the track format table 200 andincludes the track format code 202 in the field 314 in the cache controlblock 300 _(i). The track format code valid flag 316 is set (at block716) to valid and the track format table support information 318 is set(at block 718) to indicate the track format table 200 includes a trackformat code 202 for the track format metadata of the track. From block708 or 718, control proceeds to block 720 to destage the track metadatafrom the memory 138 if modified or discard if not modified.

With the operations of FIG. 7, the track format information may beindicated in the cache control block 300 _(i) with a track format code202 having a limited number of bits to index track format metadata 204describing track layout in a track format table 200, where the trackmetadata itself would not fit into the cache control block 300 _(i). Forfuture read/write accesses, if a valid track format code 314 isprovided, then the cache manager 142 may use that code 314 to obtainwith low latency the track format metadata 204 from the track formattable 200 without having to read the track metadata from the storage 104and process to determine the track format. Further, the track formattable support information 318 is updated to indicate that the trackformat table 200 supports or does not support the track format metadataof the track. This track format table support information 318 may besubsequently used to determine whether to rebuild the track metadata fora track to determine if there is a track format code 202 for the trackformat metadata if the track metadata is invalidated.

FIG. 8 illustrates an embodiment of operations performed by the cachemanager 142 to invalidate track format information, such as track formatcodes 312 saved for tracks in cache 140. Upon initiating (at block 800)an operation to invalidate a metadata track, a determination is made (atblock 802) of tracks having metadata in the metadata track toinvalidate. If (at block 804) the cache control block directory 300includes cache control blocks 300 _(i) for any of the determined trackshaving metadata in the metadata track to invalidate, then the trackformat code valid flag 316 in each of the determined cache controlblocks is set (at block 806) to indicate the track format code 314 isinvalid. If (at block 1204) the cache control block directory 300 doesnot include cache control blocks for any of the determined tracks orafter setting (at block 806) the valid flag 316 to invalid, controlends. After block 806, the previously determined track format tablesupport information 318 would be available to indicate whether it wouldbe worthwhile to utilize processing resources to access or rebuild thetrack metadata to determine whether the track format table 200 includesa track format code 202 that can be used when subsequently processingrequests to the track.

FIG. 9 illustrates an embodiment of the storage system 102 of FIG. 1 asincluding a first and second processing nodes 900 a, 900 b, which mayeach include a processing complex 136 and memory 138 as described withrespect to FIG. 1. The first 900 a and second 900 b processing nodeseach include a cache 902 a, 902 b, respectively, such as cache 140described with respect to FIG. 1, and a non-volatile storage (“NVS”) 904a, 904 b to backup modified tracks from the other cache 902 b, 902 a.For instance NVS 904 a would backup modified tracks in the cache 902 bin the second processing node 900 b and NVS 904 b would backup modifiedtracks in the cache 902 a in the first processing node 900 a. In thisway, the NVSs 904 a, 904 b backup modified tracks on different powerboundaries. Each processing node 900 a, 900 b further maintains afailover manager 906 a, 906 b to determine whether to failover to theother processing node 900 b, 900 a. Because each processing node 900 a,900 b may be on a separate power boundary, the NVS 904 a, 904 b in oneprocessing node 900 a, 900 b provides backup storage for the modifiedtracks in the cache 902 b, 902 a of the other processing node 900 b, 900a to be made available in case the other processing node experiencesfailure or data loss/corruption.

FIG. 10 illustrates an embodiment of operations performed by the cachemanager 142 and/or failover manager 906 a, 906 b to update the trackformat table support information 318 when performing a failover. Uponinitiating (at block 1000) an operation to failover from a secondprocessing node 900 b to a first processing node 900 a including thecache 902 a and a non-volatile storage (NVS) 904 a backing-up modifiedtracks in the second cache 902 b in the second processing node 900 b,the failover manager 906 a copies (at block 1002) the tracks in thefirst NVS 904 a, comprising modified tracks in the second cache 902 b inthe second processing node 900 b, to the first cache 902 a. The cachemanager 142 generates (at block 1004) a cache control block 300 _(i) foreach of the tracks copied to the first cache 902 a from the first NVS902 b and sets (at block 1006) the valid flag 316 in each of thegenerated cache control blocks 300 _(i) to invalid because no trackformat code has yet been determined for these tracks added to the cache902 a. Indication is made (at block 1008) in the track format tablesupport information 318 that no determination was made whether the trackformat metadata for the copied tracks is included in the track formattable 200.

FIG. 11 illustrates an embodiment of operations performed by the cachemanager 142 to determine whether to expend the effort and resources torebuild track metadata for a track and determine whether the trackformat table 200 provides a track format code 202 for the track. In oneembodiment, this operation to determine whether to determine a trackformat code may be performed in response to returning fail on the firstchannel, at block 504 in FIG. 5. In alternative embodiments, thisoperation may be performed at other stages than after returning fail onthe first fast channel, e.g., bus interface 116, 118, 128. Uponinitiating (at block 1100) the operation to determine the track formatcodes 202 for tracks having an invalid track format code, such as if thevalid flag 316 indicates invalid, the cache manager 142 determines (atblock 1102) whether the track format table support information 318indicates that there may be a valid track format code 202 for the trackformat metadata, such as if no determination was made whether the trackformat table 200 includes the track format metadata for the track orthat the track format table 200 previously included the track formatcode 202 for the track. If so, then the cache manager 142 rebuilds (atblock 1104) the track metadata for the track including the track formatmetadata. The cache manager 142 then performs (at block 1106) theoperations at blocks 702-718 in FIG. 7 to determine whether there is atrack format code for the rebuilt track format metadata to include inthe cache control block and to indicate track format table supportinformation.

If (at block 1102) the track format table support information 318indicates that the track format code 202 was not previously determinedbecause the track format table 200 did not provide a track format code202 for the track format metadata, then control ends without trying todetermine whether the track format table 200 includes a track formatcode 202.

With the described embodiments, the cache manager 142 will expend thetime and resources to rebuild the track metadata and try to determine atrack format code 202 for the rebuilt track metadata if the track formattable support information 318 indicates that there is a possibility thetrack format table 200 would have a code 202 for the track formatmetadata. If there is not a possibility, such as if a determination wasmade that the track format table 200 does not provide a code 202, thenthe cache manager 142 will not expend the resources to try to determinethe track format code 202. However, if there is a possibility the trackformat table 200 has a code, such as if a code 202 was previouslydetermined for the track format metadata or there was no determinationmade whether the track format table 200 had the code 202 when the trackformat code was invalidated, such as during a failover (FIG. 1), thenthe cache manager 142 makes the effort to determine the track formatcode 202 to use for later read or write operations to reduce the latencyof processing subsequent read or write operations.

The present invention may be implemented as a system, a method, and/or acomputer program product. The computer program product may include acomputer readable storage medium (or media) having computer readableprogram instructions thereon for causing a processor to carry outaspects of the present invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Java, Smalltalk, C++ or the like,and conventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The computational components of FIG. 1, including the host 100, storagesystem 102, and processing nodes 900 a, 900 b may be implemented in oneor more computer systems, such as the computer system 1202 shown in FIG.12. Computer system/server 1202 may be described in the general contextof computer system executable instructions, such as program modules,being executed by a computer system. Generally, program modules mayinclude routines, programs, objects, components, logic, data structures,and so on that perform particular tasks or implement particular abstractdata types. Computer system/server 1202 may be practiced in distributedcloud computing environments where tasks are performed by remoteprocessing devices that are linked through a communications network. Ina distributed cloud computing environment, program modules may belocated in both local and remote computer system storage media includingmemory storage devices.

As shown in FIG. 12, the computer system/server 1202 is shown in theform of a general-purpose computing device. The components of computersystem/server 1202 may include, but are not limited to, one or moreprocessors or processing units 1204, a system memory 1206, and a bus1208 that couples various system components including system memory 1206to processor 1204. Bus 1208 represents one or more of any of severaltypes of bus structures, including a memory bus or memory controller, aperipheral bus, an accelerated graphics port, and a processor or localbus using any of a variety of bus architectures. By way of example, andnot limitation, such architectures include Industry StandardArchitecture (ISA) bus, Micro Channel Architecture (MCA) bus, EnhancedISA (EISA) bus, Video Electronics Standards Association (VESA) localbus, and Peripheral Component Interconnects (PCI) bus.

Computer system/server 1202 typically includes a variety of computersystem readable media. Such media may be any available media that isaccessible by computer system/server 1202, and it includes both volatileand non-volatile media, removable and non-removable media.

System memory 1206 can include computer system readable media in theform of volatile memory, such as random access memory (RAM) 1210 and/orcache memory 1212. Computer system/server 1202 may further include otherremovable/non-removable, volatile/non-volatile computer system storagemedia. By way of example only, storage system 1213 can be provided forreading from and writing to a non-removable, non-volatile magnetic media(not shown and typically called a “hard drive”). Although not shown, amagnetic disk drive for reading from and writing to a removable,non-volatile magnetic disk (e.g., a “floppy disk”), and an optical diskdrive for reading from or writing to a removable, non-volatile opticaldisk such as a CD-ROM, DVD-ROM or other optical media can be provided.In such instances, each can be connected to bus 1208 by one or more datamedia interfaces. As will be further depicted and described below,memory 1206 may include at least one program product having a set (e.g.,at least one) of program modules that are configured to carry out thefunctions of embodiments of the invention.

Program/utility 1214, having a set (at least one) of program modules1216, may be stored in memory 1206 by way of example, and notlimitation, as well as an operating system, one or more applicationprograms, other program modules, and program data. Each of the operatingsystem, one or more application programs, other program modules, andprogram data or some combination thereof, may include an implementationof a networking environment. The components of the computer 1202 may beimplemented as program modules 1216 which generally carry out thefunctions and/or methodologies of embodiments of the invention asdescribed herein. The systems of FIG. 1 may be implemented in one ormore computer systems 1202, where if they are implemented in multiplecomputer systems 1202, then the computer systems may communicate over anetwork.

Computer system/server 1202 may also communicate with one or moreexternal devices 1218 such as a keyboard, a pointing device, a display1220, etc.; one or more devices that enable a user to interact withcomputer system/server 1202; and/or any devices (e.g., network card,modem, etc.) that enable computer system/server 1202 to communicate withone or more other computing devices. Such communication can occur viaInput/Output (I/O) interfaces 1222. Still yet, computer system/server1202 can communicate with one or more networks such as a local areanetwork (LAN), a general wide area network (WAN), and/or a publicnetwork (e.g., the Internet) via network adapter 1224. As depicted,network adapter 1224 communicates with the other components of computersystem/server 1202 via bus 1208. It should be understood that althoughnot shown, other hardware and/or software components could be used inconjunction with computer system/server 1202. Examples, include, but arenot limited to: microcode, device drivers, redundant processing units,external disk drive arrays, RAID systems, tape drives, and data archivalstorage systems, etc.

The terms “an embodiment”, “embodiment”, “embodiments”, “theembodiment”, “the embodiments”, “one or more embodiments”, “someembodiments”, and “one embodiment” mean “one or more (but not all)embodiments of the present invention(s)” unless expressly specifiedotherwise.

The terms “including”, “comprising”, “having” and variations thereofmean “including but not limited to”, unless expressly specifiedotherwise.

The enumerated listing of items does not imply that any or all of theitems are mutually exclusive, unless expressly specified otherwise.

The terms “a”, “an” and “the” mean “one or more”, unless expresslyspecified otherwise.

Devices that are in communication with each other need not be incontinuous communication with each other, unless expressly specifiedotherwise. In addition, devices that are in communication with eachother may communicate directly or indirectly through one or moreintermediaries.

A description of an embodiment with several components in communicationwith each other does not imply that all such components are required. Onthe contrary a variety of optional components are described toillustrate the wide variety of possible embodiments of the presentinvention.

When a single device or article is described herein, it will be readilyapparent that more than one device/article (whether or not theycooperate) may be used in place of a single device/article. Similarly,where more than one device or article is described herein (whether ornot they cooperate), it will be readily apparent that a singledevice/article may be used in place of the more than one device orarticle or a different number of devices/articles may be used instead ofthe shown number of devices or programs. The functionality and/or thefeatures of a device may be alternatively embodied by one or more otherdevices which are not explicitly described as having suchfunctionality/features. Thus, other embodiments of the present inventionneed not include the device itself.

The foregoing description of various embodiments of the invention hasbeen presented for the purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed. Many modifications and variations are possible in lightof the above teaching. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto. The above specification, examples and data provide acomplete description of the manufacture and use of the composition ofthe invention. Since many embodiments of the invention can be madewithout departing from the spirit and scope of the invention, theinvention resides in the claims herein after appended.

1-23. (canceled)
 24. A computer program product for managing metadatafor tracks in storage cached in a cache, the computer program productcomprising a computer readable storage medium having computer readableprogram code embodied therein that is executable to perform operations,the operations comprising: maintaining a track format table providingtrack format codes for different track format metadata; determiningwhether there is a possibility that a track format table has a validtrack format code for track format metadata for a track; and rebuildingtrack format metadata for the track in response to determining thatthere is a possibility the track format table has a track format codefor the track format metadata for the track.
 25. The computer programproduct of claim 24, wherein the track format metadata is not rebuilt inresponse to determining that there is no possibility the track formattable has the valid track format code for the track.
 26. The computerprogram product of claim 24, wherein the determining whether there isthe possibility the track format table has the valid track format codecomprises determining at least one of: that no determination was madewhether the track format table includes track format metadata for thetrack; and that the track format table includes the track format codefor the track.
 27. The computer program product of claim 24, wherein thedetermining whether there is the possibility that the track format tablehas the valid track format code for track format metadata for a trackand rebuilding the track format metadata for the track are performed inresponse to a request to access track format metadata for the track whenthe request to access the track failed on a first channel and wasretried on a second channel.
 28. The computer program product of claim24, wherein the operations further comprise: determining whether thetrack format table has a track format matching the rebuilt track formatmetadata; determining a track format code in the track format table forthe track format matching the rebuilt track format metadata; includingthe determined track format code in a cache control block for the track;and indicating that there is a possibility that the track format tableincludes the track format code for the track in response to determiningthe track format code.
 29. The computer program product of claim 24,wherein the operations further comprise: determining whether the trackformat table has a track format matching the rebuilt track formatmetadata; determining a track format code in the track format table forthe track format matching the rebuilt track format metadata; andindicating that the track format table does not include the track formatcode for the track format metadata for the track in response todetermining that the track format table does not have a track formatmatching the rebuilt track format metadata.
 30. The computer programproduct of claim 24, wherein a cache control block for the trackindicates whether there is a possibility that a track format table has avalid track format code for track format metadata for the track.
 31. Asystem for managing metadata for tracks in a storage, comprising: aprocessor; a cache; and a computer readable storage medium havingcomputer readable program code embodied therein that when executed bythe processor performs operations, the operations comprising:maintaining a track format table providing track format codes fordifferent track format metadata; determining whether there is apossibility that a track format table has a valid track format code fortrack format metadata for a track; and rebuilding track format metadatafor the track in response to determining that there is a possibility thetrack format table has a track format code for the track format metadatafor the track.
 32. The system of claim 31, wherein the track formatmetadata is not rebuilt in response to determining that there is nopossibility the track format table has the valid track format code forthe track.
 33. The system of claim 31, wherein the determining whetherthere is the possibility the track format table has the valid trackformat code comprises determining at least one of: that no determinationwas made whether the track format table includes track format metadatafor the track; and that the track format table includes the track formatcode for the track.
 34. The system of claim 31, wherein the determiningwhether there is the possibility that the track format table has thevalid track format code for track format metadata for a track andrebuilding the track format metadata for the track are performed inresponse to a request to access track format metadata for the track whenthe request to access the track failed on a first channel and wasretried on a second channel.
 35. The system of claim 31, wherein theoperations further comprise: determining whether the track format tablehas a track format matching the rebuilt track format metadata;determining a track format code in the track format table for the trackformat matching the rebuilt track format metadata; including thedetermined track format code in a cache control block for the track; andindicating that there is a possibility that the track format tableincludes the track format code for the track in response to determiningthe track format code.
 36. The system of claim 31, wherein theoperations further comprise: determining whether the track format tablehas a track format matching the rebuilt track format metadata;determining a track format code in the track format table for the trackformat matching the rebuilt track format metadata; and indicating thatthe track format table does not include the track format code for thetrack format metadata for the track in response to determining that thetrack format table does not have a track format matching the rebuilttrack format metadata.
 37. The system of claim 31, wherein a cachecontrol block for the track indicates whether there is a possibilitythat a track format table has a valid track format code for track formatmetadata for the track.
 38. A method for managing metadata for tracks ina storage cached in a cache, comprising: maintaining a track formattable providing track format codes for different track format metadata;determining whether there is a possibility that a track format table hasa valid track format code for track format metadata for a track; andrebuilding track format metadata for the track in response todetermining that there is a possibility the track format table has atrack format code for the track format metadata for the track.
 39. Themethod of claim 38, wherein the track format metadata is not rebuilt inresponse to determining that there is no possibility the track formattable has the valid track format code for the track.
 40. The method ofclaim 38, wherein the determining whether there is the possibility thetrack format table has the valid track format code comprises determiningat least one of: that no determination was made whether the track formattable includes track format metadata for the track; and that the trackformat table includes the track format code for the track.
 41. Themethod of claim 38, further comprising: determining whether the trackformat table has a track format matching the rebuilt track formatmetadata; determining a track format code in the track format table forthe track format matching the rebuilt track format metadata; includingthe determined track format code in a cache control block for the track;and indicating that there is a possibility that the track format tableincludes the track format code for the track in response to determiningthe track format code.
 42. The method of claim 38, further comprising:determining whether the track format table has a track format matchingthe rebuilt track format metadata; determining a track format code inthe track format table for the track format matching the rebuilt trackformat metadata; and indicating that the track format table does notinclude the track format code for the track format metadata for thetrack in response to determining that the track format table does nothave a track format matching the rebuilt track format metadata.
 43. Themethod of claim 38, wherein a cache control block for the trackindicates whether there is a possibility that a track format table has avalid.